NO344828B1 - Absorbent composition containing molecules with a hindered amine and a metal sulfonate, phosphonate or carboxylate structure for acid gas scrubbing process - Google Patents

Description

The present invention relates to a method for selective absorption of H2S from gaseous mixtures as stated in claim 1. The invention also relates to an absorbent composition and its use for selective absorption of H2S from an H2S- and other acid component-containing mixtures.

DESCRIPTION OF RELATED ART

It is well known in the art to treat gases and liquids, such as mixtures containing acid gases, including CO2, H2S, CS2, HCN, COS and oxygen and sulfur derivatives of C1-C4 hydrocarbons with amine solutions to remove these acid gases. The amine is usually contacted with the acid gases and liquids as an aqueous solution containing the amine in an absorption tower with the aqueous amine solution brought into countercurrent contact with the acid fluid.

The treatment of acid gas mixtures containing, among other things, CO2 and H2S with amine solutions typically leads to the simultaneous removal of significant amounts of both CO2 and H2S. For example, in such a process, generally referred to as the "aqueous amine process", relatively concentrated amine solutions are used. A recent improvement to this process involves the use of sterically hindered amines, as described in USP 4112052, to achieve almost complete removal of acid gases, such as CO2 and H2S. This type of process can be used where the partial pressures for CO2 and related gases are low. Another process that is often used for specialized applications, where the partial pressure of CO2 is very high, and/or where many acid gases are present, e.g. H2S, COS, CH3SH and CS2, involves the use of an amine in combination with a physical absorbent, generally referred to as "the non-aqueous solvent process". An improvement of this process involves the use of sterically hindered amines and organic solvents as the physical absorbent, as described in USP 4112051. Other methods and compositions for such removal of H2S are known from US 3042483 A and US 3532637 A.

However, it is often desirable to treat acid gas mixtures containing both CO2 and H2S, in order to selectively remove H2S from the mixture, thereby minimizing the removal of CO2. Selective removal of H2S leads to a relatively high H2S/CO2 ratio in the separated acid gas, which facilitates conversion of H2S to elemental sulfur using the Claus process.

The typical reactions of aqueous secondary and tertiary amines with CO2 and H2S can be represented as follows:

wherein each R is an organic radical which may be the same or different and may be substituted with a hydroxy group. The above reactions are reversible, and the partial pressures for both CO2 and H2S are thus important in determining the extent to which the above reactions will occur.

While selective H2S removal is applicable to a number of gas processing operations, including the treatment of hydrocarbon gases from shale pyrolysis, refinery gas, and natural gas having a low H2S/CO2 ratio, it is desirable in the treatment of gases in which the partial pressure of H2S is relatively low compared to the for CO2, due to that the amine's capacity to absorb H2S from the latter type of gases is very low. Examples of gases with relatively low partial pressures of H2S include synthetic gases made by gold gasification, tail gas from sulfur plants and fuel gases with low Joule values encountered in refineries where heavy residual oil is thermally converted to lower molecular weight liquids and gases.

Although solutions of primary and secondary amines such as monoethanolamine (MEA), diethanolamine (DEA), dipropanolamine (DPA) and hydroxyethoxyethylamine (DGA) are known to absorb both H2S and CO2 gas, they have not proven particularly satisfactory for preferential absorption of H2S over exclusion of CO2, because the amines undergo a facile reaction with CO2 to form carbamates, as shown in Equations 5 and 6.

Diisopropanolamine (DIPA) is relatively unique among secondary amine alcohols in that it has been used industrially, alone or with a physical solvent such as sulfolane, for the selective removal of H2S from gases containing H2S and CO2, but the contact time must be kept relatively short to take advantage of the rapid reaction of H2S with the amine, compared to the rate of CO2 reaction shown in equations 2 and 4 above.

In 1950, Frazier and Kohl, Ind. and Eng. Chem., 42, 2288 (1950), that the tertiary amine, methyldiethanolamine (MDEA), has a high degree of selectivity against H2S absorption in relation to CO2. This greater selectivity was attributed to the relatively slow chemical reaction of CO2 with tertiary amines, compared to the fast chemical reaction of H2S. However, the commercial utility of MDEA is limited due to its limited capacity for H2S loading and its limited ability to reduce the H2S content to the level at low pressures necessary for the treatment of e.g. synthetic gases made by coal gasification.

Recently, UK patent publication number 2017524A by Shell, has shown that aqueous solutions of dialkyl monoalkanolamines, and in particular diethyl monoethanolamine (DEAE), have higher selectivity and capacity for H2S removal at higher loading levels than MDEA solutions. Nevertheless, even DEAE is not very effective for the low H2S loading frequency encountered in industry. Also, DEAE has a boiling point of 161 °C, and as such it is characterized as being an amino alcohol with a low boiling point and relatively high volatility. Such substances with high volatility will under most gas scrubbing conditions lead to large material losses, with consequent loss of economic benefits.

US Patent Number 4405581; 4405583 and 44055585 show the use of highly sterically hindered amine compounds for the selective removal of H 2 S in the presence of CO 2 . Compared to aqueous methyldiethanolamine (MDEA), highly sterically hindered amines lead to much higher selectivities at higher H2S loadings.

USP 4112052 is directed to a process for removing CO2 from acid gases using an aqueous amine scrubbing solution. The amines used are sterically hindered amines, containing at least one secondary amine group attached to either a secondary or a tertiary carbon atom, or a primary amine group attached to a tertiary carbon atom. The amines are chosen to be at least partially soluble in the solvent used, i.e. water.

USP 4376102 shows that acid gases containing CO2 are removed from normally gaseous mixtures by absorption of CO2 from the gaseous mixture, using an aqueous solution comprising a basic alkali metal salt or hydroxide containing (1) at least one diamine alcohol of the formula

wherein R and R1 are each independently a C1-C6 alkyl group and either R or R1 or both R and R1 have a pendant hydroxyl group and (2) an amino acid. The basic alkali metal salt or hydroxide is selected from the group consisting of alkali metal bicarbonates, carbonates, hydroxides, borates, phosphates and mixtures thereof. See also USP 4376101; USP 4581209; USP 4217238.

USP 4525294 is directed to amino acid mixtures, their alkali metal salts and processes for their preparation. The processes involve the reductive condensation of glycine or alanine and their alkali metal salts with a ketone in the presence of a reducing agent, such as hydrogen, and a catalytically effective amount of a hydrogenation catalyst. Thus, a reaction as follows appears:

wherein R is hydrogen or methyl, X is hydrogen or an alkali metal such as sodium or potassium, R' and R'' are selected from the group consisting of

a) substituted or unsubstituted linear or branched alkyl radicals having 1 to 20 carbon atoms; or

b) substituted or unsubstituted alkylene radicals each having 3 to 6 carbon atoms and combining to form a cyclic ring;

c) substituted or unsubstituted cycloalkyl radicals having from 4 to 8 ring carbon atoms;

d) substituted or unsubstituted hydroxyl alkyl radicals, linear or branched, having 1 to 20 carbon atoms; or

e) substituted or unsubstituted arylalkyl radicals having from 7 to 20 carbon atoms;

and R''' is hydrogen or a substituted or unsubstituted linear alkyl radical having from 1 to 20 carbon atoms, or mixtures of hydrogen and such alkyl radicals.

USP 4759866 discloses primary sterically hindered amino acids of the formula

wherein R 1 and R 2 are independently selected from CH 3 , C 2 H 5 and C 3 H 7 , and R 3 and R 4 are independently hydrogen and CH 3 and n are zero, 2 or 3, for use as promoters for alkali metal salts in acid gas scrubbing.

USP 5602279 is directed to a gas treatment composition prepared by reacting 2-amino-2-methyl-1-propanol with KOH, diluting with water and adding K 2 CO 3 and a vanadium corrosion inhibitor. The acid gas scrubbing solution contains

USP 4618481 is directed to an absorbent composition comprising a highly hindered amine compound and an amine salt for the absorption of H 2 S from gaseous mixtures. The highly sterically hindered amine compound can be a secondary amine ether alcohol, a disecondary amino ether and mixtures thereof. Amine salts may be the reaction product of the above-mentioned strongly sterically hindered amine compound, a tertiary amine compound, such as tertiary alkanolamines, triethanolamines and mixtures thereof and a strong acid, or a thermally decomposable salt of a strong acid, i.e. ammonium salt or a component capable of to form a strong acid and mixtures thereof. Suitable strong acids include inorganic acids such as sulfuric acid, sulfuric acid, phosphoric acid, phosphoric acid, pyrophosphoric acid, an organic acid such as acetic acid, formic acid, adipic acid, benzoic acid, etc. Suitable salts for these acids include ammonium salts, e.g. ammonium sulphate, ammonium sulphite, ammonium phosphate and mixtures thereof. Preferably, ammonium sulphate (a salt) or SO2 (a precursor of an acid) is used as reactant with the amine. Suitable amine salts are those which are non-volatile under conditions used to regenerate the absorbent composition.

USP 4892674 is directed to an absorbent composition comprising an alkaline absorbent solution containing a non-hindered amine and an additive of a strongly hindered amine salt and/or a strongly hindered amino acid and the use of the absorbent for the selective removal of H2S from gaseous streams. The amine salt is the reaction product of an alkaline highly hindered amine compound and a strong acid or a thermally decomposable salt of a strong acid, i.e. ammonium salt. Suitable strong acids include inorganic acids such as sulfuric acid, sulfuric acid, phosphoric acid, phosphoric acid, pyrophosphoric acid; organic acids such as acetic acid, formic acid, adipic acid, benzoic acid, etc. Suitable salts include the ammonium salts, e.g. ammonium sulphate, ammonium sulphite, ammonium phosphate and mixtures thereof.

DESCRIPTION OF THE FIGURE

Figure 1 is a diagrammatic flow diagram illustrating an absorption regeneration unit for the selective removal of H 2 S from gaseous streams containing H 2 S and CO 2 .

SUMMARY OF THE INVENTION

The present invention is directed to an absorbent comprising a metal sulphonate, metal phosphonate or metal carboxylate of hindered amines and to a method for removing H2S from gaseous mixtures containing H2S, using said absorbents.

DETAILED DESCRIPTION OF THE INVENTION

An absorbent composition comprising at least one of metal sulfonate, metal phosphonate, metal phosphate, metal sulfamate, metal phosphoramidate, or metal carboxylate, of at least one hindered secondary or tertiary amine, wherein the metal sulfonate, sulfomate, phosphonate, phosphate, or phosphoramidate is attached to the nitrogen of the amine through a group containing at least one chained carbon, preferably 1 to 4 chained carbons, more preferably alkylene group with two to four chained carbons, and the metal carboxylate is attached to the nitrogen of the amine through an alkylene group containing 2 or more chained carbons.

The absorbents are generally represented by the following formulas:

wherein R1, R2, R3 and R4 are the same or different and selected from H, C1-C9 substituted or unsubstituted straight or C3-C9 substituted or unsubstituted branched chain alkyl, C3-C9 cycloalkyl, C6-C9 aryl, alkylaryl , arylalkyl, C2-C9 straight or branched hydroxyalkyl, cycloalkyl and mixtures thereof provided that both R1 and R2 are not hydrogen, and wherein when n is 2 or more, R3 and R4 on adjacent carbon or carbons separated by one or more carbons may be a cycloalkyl or aryl ring, and wherein when substituted the substituents are heteroatom-containing substituents, preferably

group wherein R5 and R6 are the same or different and selected from H, C1-C9 straight or C3-C9 branched chain alkyl, C3-C9 cycloalkyl, C6-C9 aryl, alkylaryl, arylalkyl, C2 to C9 straight or branched chain hydroxyalkyl, cycloalkyl and mixtures thereof, provided that R5 and R6 are not both H, and further wherein optionally when R1 is H, and n is 2 or more, R2 and R3 or R4 on the carbon at least one carbon removed from the nitrogen of the amine may form a ring ,

n is an integer of 1 or more, preferably 1 to 4, more preferably 2 to 4, and wherein, when n is at least 2, the absorbent may be a metal carboxylate of the amine,

metal cation is one or more monovalent, divalent or trivalent metal cations sufficient to satisfy the valence requirements for the anion or anion cluster, preferably magnesium, barium, aluminium, iron, lithium, potassium, calcium, nickel, cobalt. Salts formed from divalent cations can be half salts or full salts. Salts formed from trivalent cations can be one-third, two-thirds or full salts. By anion cluster is meant two or more anions where the valence requirements are satisfied by e.g. a single divalent or trivalent metal cation.

Preferably, R1 and R2 are the same or different and selected from H, C4-C6 substituted or unsubstituted straight or branched chain alkyl, cyclic alkyl, C6-C7 aryl, alkylaryl, arylalkyl, C4-C6 straight or branched chain hydroxyalkyl, cycloalkyl and mixtures thereof, more preferably C4 to C6 straight or branched chain alkyl, most preferably tertiary butyl, provided that both R1 and R2 are not hydrogen.

Examples of preferred materials are of the formula:

The absorbents described above exhibit high selectivity for H2S and other gaseous acid component(s) removal from mixtures of said gaseous acid components, non-acid components, and CO2 and retain their high selectivity and load capacity, even after regeneration.

The method used in particular for the selective absorption of gaseous acid components, e.g. H2S from a normally gaseous mixture containing gaseous acid components, e.g. H2S, and non-acid components and CO2, include to:

a) put said normally gaseous mixture in contact with an amine-containing absorbent solution as stated in claim 1, characterized as being capable of selective absorption of one or more gaseous acid components, e.g. H2S from said mixture;

b) regenerating, at least partially, said absorbent solution containing absorbent gaseous acid components, e.g. H2S; and

c) recirculating the regenerated solution for the selective absorption of one or more gaseous acid components, e.g. H2S by contacting as in step (a).

Preferably, the regeneration step is carried out by heating and stripping, and more preferably by heating and stripping with steam.

The term "absorbent solution" as used herein includes, but is not limited to solutions in which the amine compound is dissolved in a solvent selected from water or a physical absorbent, or mixtures thereof. Solvents which are physical absorbents (as opposed to the amine compounds, which are chemical absorbents) are e.g. described in USP 4112051, includes e.g. aliphatic acid amides, N-alkylated pyrrolidones, sulphones, sulphoxides, glycols and mono- and dieters thereof. The preferred physical absorbents herein are sulfones, and most especially sulfolane. The preferred liquid medium comprises water.

The absorbent solution ordinarily has a concentration of the amine compound of about 0.1 to 6 mol/liter of the total solution, and preferably 1 to 4 mol/liter, depending primarily on the specific amine compound used and the solvent system used. If the solvent system is a mixture of water and a physical absorbent, the typical effective amount of the physical absorbent used may vary from 0.1 to 5 mol/liter of total solution, and preferably from 0.5 to 3 mol/liter, mainly depending on the type of amine compound used. The dependence on the concentration of the amine compound for the particular compound used is significant, because that increasing the concentration of the amine compound may reduce the basicity of the absorbent solution, thereby adversely affecting its selectivity for H2S removal, especially if the amine compound has a specific aqueous solubility limit which will determine maximum concentration levels within the range given above. It is therefore important that the correct concentration level suitable for each particular amine compound is maintained to ensure satisfactory results.

The solution of this invention can include a number of additives that are typically used in selective gas removal processes, e.g. anti-foaming agents, antioxidants, corrosion inhibitors, etc. The amount of these additives will typically be in the range so that they are effective, i.e. an effective amount.

Also, the amino compounds described herein can be combined with other amine compounds as a mixture. The ratio of the respective amine compounds can vary widely, e.g. from 1 to 99 percent by weight of the amine compounds described herein.

Three characteristics, which are of utmost importance in determining the effectiveness of the amine compounds here for H2S removal, are "selectivity", "loading" and "capacity". The term "selectivity" as used throughout the specification is defined as the following molar ratio fraction:

The higher this fraction, the greater the selectivity of the absorbent solution for H2S in the gas mixture.

The term "loading" means the concentration of H2S and CO2 gases that are physically dissolved and chemically combined in the absorbent solution as expressed in moles of gas per mole of amine. The best amine compounds are those that exhibit good selectivity, up to a relatively high loading level. The amine compounds used in the practice of the present invention typically have a "selectivity" of not significantly less than 10 at a "loading" of 0.1 mol, preferably a "selectivity" of not significantly less than 10 at a loading of 0.2 or several moles of H2S and CO2 per mole of the amine compound.

"Capacity" is defined as moles of H2S loaded in the absorbent solution at the end of the absorption step minus moles of H2S loaded in the absorbent solution at the end of the desorption step. High capacity makes it possible to reduce the amount of amine solution to be circulated and use less heat or steam during regeneration.

The acid gas mixture here necessarily includes H2S, and may optionally include other gases, such as CO2, N2, CO4, H2, CO, H2O, COS, HCN, C2H4, NH3 etc. Such gas mixtures are often found in combustion gases, refinery gases, city gas, natural gas, syngas, water gas, propane, propylene, heavy hydrocarbon gases, etc. The absorbent solution here is particularly effective when the gas mixture is a gas, e.g. obtained from shale oil retorts, coal condensation or gasification, gasification of heavy oil with steam, air/steam or oxygen/steam, thermal conversion of heavy residual oil to lower molecular weight liquids and gases, e.g. fluid coking plant, flexic coking plant or delayed coking plant or in cleaning operations for tail gas from sulfur plants.

The absorption step of this invention generally involves contacting the normally gaseous stream with the absorbent solution in any suitable contacting container. In such processes, this normally gaseous mixture containing H 2 S and CO 2 , from which H 2 S as well as other acid components such as carbon disulphide, carbonyl sulphide and oxygen and sulfur derivatives of C1-C4 hydrocarbons, can be selectively removed by bringing into intimate contact with the absorbent solution using conventional means such as a tower or a container packed with e.g. rings or sieve plates or a bubble reactor. Other acid gas components will also be removed.

In a typical mode of practicing the invention, the absorption step is carried out by feeding the normally gaseous mixture into the lower part of the absorption tower, while fresh absorbent solution is fed to the upper region of the tower. The gaseous mixture, mainly freed of H 2 S, exits from the upper part of the tower, and the loaded absorbent solution, containing the selectively absorbed H 2 S, leaves the tower near or at its bottom. Preferably, the inlet temperature of the absorbent solution during the absorption step is in the range of from about 20°C to about 100°C, and more preferably from 30°C to about 60°C. Pressure can vary widely; acceptable pressures are between 5 and 2000 psia, preferably 20 to 1500 psia, and most preferably 25 to 1000 psia in the absorption unit. The contact takes place under conditions such that H2S is selectively absorbed by the solution. The absorption conditions and equipment are designed to minimize the residence time of the liquid in the absorption unit to reduce CO2 uptake, while at the same time maintaining sufficient residence time for the gas-liquid mixture to absorb a maximum amount of the H2S gas. The amount of liquid required to circulate to achieve a given degree of H2S removal will depend on the chemical structure and basicity of the amine compound, and on the partial pressure of H2S in the feed gas. Gas mixtures with low partial pressures, such as those encountered in thermal conversion processes, will require more liquid under the same absorption conditions than gases with higher partial pressures, such as shale oil retort gases.

A typical procedure for the selective H2S removal phase of the process comprises selective absorption of H2S via a countercurrent contacting of the gaseous mixture, containing H2S and CO2, with the solution of the amine compound in a column containing several trays at a low temperature, e.g. below 45 °C, and at a gas velocity of at least about 9.144 cm/sec (based on "active" or vented tray surface), depending on the operating pressure of the gas, said tray column having fewer than 20 contacting trays, e.g. with 4 to 16 trays typically used.

After contacting the normally gaseous mixture with the absorbent solution, which becomes saturated or partially saturated with H2S, the solution can be at least partially regenerated, so that it can be recycled back to the absorption unit. As with absorption, the regeneration can take place in a single liquid phase. Regeneration or desorption of the absorbent solution can be carried out in conventional ways, such as reducing the pressure of the solution or increasing the temperature to a point where the absorbent H2S is degassed, or by bypassing the solution in a vessel of similar construction to that used in the absorption step, in the upper part of the container, and pass an inert gas such as air or nitrogen, or preferably steam upwards through the container. The temperature of the solution during the regeneration step should range from about 50°C to about 170°C, and preferably from about 80°C to 120°C, and the pressure of the solution during regeneration should range from about 0.5 to about 100 psia, preferably 1 to about 50 psia. The absorbent solution, after being purged of at least a portion of the H 2 S gas, can be recycled back to the absorption vessel. Refill absorbent can be added if required.

In the preferred regeneration technique, the H2S-rich solution is sent to the regenerator, where the absorbed components are stripped with steam, which is generated by repeated boiling of the solution. Pressure in the degassing vessel and stripper is typically 1 to about 50 psia, preferably 15 to about 30 psia, and the temperature is typically in the range of about 50°C to 170°C, preferably about 80°C to 120°C, stripper and degassing temperatures will of course depend on the stripper pressure, thus at about 15 to 30 psia stripper pressure, the temperature will be about 80°C to about 120°C during desorption. Heating of the solution to be regenerated can be effected in a very suitable way by means of indirect heating with low-pressure steam. However, it is also possible to use direct injection of steam.

In an embodiment for practicing the whole process here, as illustrated in figure 1, the gas mixture to be purified is supplied through line 1 through the lower part of a contacting column 2 with gas-liquid in countercurrent, the contacting column has a lower section 3 and an upper section 4 .The upper and lower sections may be separated by one or more packed layers as required. The absorbent solution as described above is supplied to the upper part of the column through a pipeline 5. The solution flowing to the bottom of the column meets the gas flowing countercurrently and dissolves H2S preferentially. The gas freed of most of the H2S exits through pipeline 6, for final use. The solution, mainly containing H2S and some CO2 flows towards the lower part of the column, from where it is discharged through pipe 7. The solution is then pumped via optional pump 8 through an optional heat exchanger and a cooler 9 deposited in pipe 7, which allows the hot solution from the regenerator 12 to exchange heat with the cooling solution from the absorption column 2 for energy saving. The solution enters via pipe 7 to a degassing container 10, equipped with a line (not shown) which vents to line 13 and is then supplied by line 11 into the upper part of the regenerator 12, which is equipped with several plates and effects the desorption of H2S and CO2 gases carried together in the solution. This acid gas is led through a pipe 13 into a condenser 14, in which cooling and condensation of water and the amine solution from the gas takes place. The gas then enters a separator 15, where further condensation is effected. The condensed solution is returned through pipe 16 to the upper part of the regenerator 12. The gas remaining from the condensation, which contains H2S and some CO2, is removed through pipe 17 for final disposal (e.g. to an aeration or combustion unit or to an apparatus which converts H2S to sulphur, such as a Claus unit or a Stretford conversion unit (not shown)).

The solution releases most of the gas it contains as it flows downward through the regenerator 12, exiting through pipe 18 at the bottom of the regenerator for transfer to a boiler 19. The boiler 19, equipped with an external heat source (e.g. steam injected through pipe 20 and the condensate exits through a second pipe (not shown)), some of this solution (mainly water) evaporates to drive further H 2 S out there. The H 2 S and the steam expelled are returned via pipe 21 to the lower section of the regenerator 12 and discharged through pipe 13 to enter the condensing stages for gas treatment. The solution that remains in the boiler 19 is withdrawn through pipe 22, cooled in the heat exchanger 9, and supplied via the action of pump 23 (optional if the pressure is sufficiently high) through pipe 5 into the absorption column 2.

Typically, a gaseous stream to be treated that has a 1:10 molar ratio of H2S:CO2 from a heavy residual oil thermal reformer, or a Lurgic coal gas that has a molar ratio of H2S:CO2 of less than 1:10, will give a acid gas having a molar ratio of H2S:CO2 of approximately 1:1, after treatment with the method of the present invention. The process herein can be used in conjunction with another H 2 S selective removal process: however, it is preferred to carry out the process of this invention by itself, since the amine compounds are extremely effective by themselves in the preferential absorption of H 2 S.

PREPARATION OF SAMPLES

Preparation of sodium tert-butylamine methylsulfonate

37% formaldehyde solution (18 g, 0.22 mol) was added to a suspension of sodium bisulfite (22 g, 0.2 mol) in water (25 mL). To this mixture was added tert-butylamine (28 ml, 19.4 g, 0.26 mol) at such a rate that the temperature of the reaction mixture did not exceed 30 °C. When the addition was complete, a still was set up and the mixture was stirred at 70 to 75°C for 10 minutes (excess tert-butylamine was distilled off) and cooled to 10-15°C. The precipitate formed was filtered, washed with methanol and dried at 20 to 25 °C to give sodium tert-butylamine methylsulfonate (30 g, 80%) as white plates, decomposing without melting above 180 to 190 °C (amine odor), 1 H NMR (DMSO-d 6 ) δ 1.02 (s, 9H), 3.32 (s, 2H); 13 C NMR δ 28.9, 49.9, 60.8.

Sodium 2-(tert-butylamine) ethylsulfonate

tert-butylamine (127 mL, 88 g, 1.2 mol) was added to a solution of sodium 2-hydroxyethyl sulfonate) (29.6 g, 0.2 mol) and disodium phosphate (1.1 g, 8 mmol) in water ( 50ml). The mixture was stirred at 240 to 245 °C (6.5 MPa) in an autoclave for 3 hours. The mixture was then cooled to 50-60 °C and concentrated to 50 ml under normal pressure. After cooling to 10 to 15 °C, the precipitate formed was filtered, washed with methanol and dried at 20 to 25 °C. Yield 10 g. The filtrate was concentrated under normal pressure to about 25 to 30 ml, which gives an additional 5.6 g of product. Total yield of sodium 2-(tert-butylamine)ethylsulfonate is 15.6 g, 38%, as white plates, dec 145 to 150 °C (becomes semi-fluid), 1H NMR (DMSO-d6) δ 1.00 ( s, 9H), 2.56 (t, J = 6.6 Hz, 2H), 2.72 (t, J = 6.6 Hz, 2H); 13 C NMR δ 28.9, 38.6, 49.6, 52.2.

3-(tert-butylamine)propylsulfonic acid

To a solution of 1,3-propanesulfone (20 g, 0.164 g) in toluene (100 mL) was added tert-butylamine (90 mL, 62.1 g, 0.85 mol). The mixture was stirred under gentle reflux for 1 hour. The precipitate was filtered, washed with diethyl ether and dried at 20 to 25 °C. The yield of 3-(tert-butylamine)propylsulfonic acid 32 g (approx. 100%), as white microcrystals, mp above 280 °C, 1H NMR (D2O) δ 1.33 (s, 9H), 2.07 (p, J = 7.6 Hz, 2H), 2.99 (t, J = 7.6 Hz, 2H), 3.15 (t, J = 7.7 Hz, 2H); 13 C NMR δ 21.3, 24.3, 39.4, 47.4, 56.5.

Sodium 3-(tert-butylamine)propylsulfonate

3-(tert-butylamine)propylsulfonic acid (18 g) was added to a solution of sodium hydroxide (3.69 g, 0.092 mol) in methanol (300 mL). The mixture was stirred until clear. The solution was removed and the solid residue was dried in vacuo to give sodium 3-(tertbutylamine)propylsulfonate (18.7 g), as white microcrystals, dec at 170 °C, 1H NMR (D2O) δ 1.08 (s, 9H), 1.80-1.90 (m, 2H), 2.64 (t, J = 7.6 Hz, 2H), 2.91-2.96(m, 2H); 13 C NMR δ 24.4, 26.9, 39.8, 48.7, 49.6.

Preparation of disodium tert-butylamine methylphosphonate

N-methylene-tert-butylamine was prepared according to the published procedure [USP 2750416] with some modifications as follows:

37% aqueous formaldehyde (89 g solution, 33 g, 1.1 mol) was added dropwise with stirring to tert-butylamine (73 g, 1 mol) and over 20 minutes and the temperature was kept below 20 °C (cooling in an ice bath ). The reaction mixture was stirred for 30 minutes at 20 to 22 °C, cooled to 5 to 10 °C, and potassium hydroxide (30 g) was added portionwise upon cooling at 15 to 20 °C. The organic layer was separated and dried over potassium hydroxide pellets. The purification that was attempted by distillation gave unsatisfactory results due to trimerization of N-methylene-tert-butylamine at elevated temperature. Purification of the crude product was achieved by distillation in the presence of catalytic p-toluenesulfonic acid (on 10 cm column, oil bath 115 to 120 °C) to give pure N-methylene-tert-butylamine in 87% yield (74 g), bp 66 to 67 °C (lit. [USP 2750416] 64-65 °C); 1 H NMR (CDCl 3 ) 1.20 (s, 9H) 7.26 (d, J = 16.0 Hz, 1H), 7.41 (d, J = 16.0 Hz, 1H).

Diethyl tert-butylamine methylphosphonate

Diethyl phosphite (41.4 g, 0.3 mol) was added to N-methylene-tert-butylamine (25.6 g, 0.3 mol) under a nitrogen atmosphere. Within 1-2 minutes the temperature in the mixture rose spontaneously up to 60-70 °C. The mixture was stirred at 80°C for 30 minutes and then at 20 to 25°C for 12 hours. The NMR test of the mixture showed pure diethyl tert-butylamine methylphosphonate, as a colorless oil, 1H NMR (CDCl3) δ 1.08 (s, 9H), 1.34 (t, J = 7.0 Hz, 6H), 2, 93 (d, J = 15.1 Hz, 2H), 4.11-4.22 (m, 4H); 13-c NMR δ 16.4 (d, J = 5.7 Hz), 28.4, 38.6 (d, J = 159.2 Hz), 50.8 (d, J = 17.8 Hz) 62.1 (d, J = 6.9 Hz). "Novel Synthesis of Aminomethythyl Phosphoric Acid", Moedritzer, K., Synthesis in Inorganic and Metal-Organic Chemistry, 1972, 2, 317.

Tert-butylamine methylphosphonic acid

The above crude ester (65 g) was added dropwise to concentrated hydrochloric acid (200 ml). The mixture was stirred at 90 °C for 20 hours. The mixture was concentrated in vacuo until solid, and ethanol (300 mL) was added to the residue. The mixture was cooled to -5°C for 30 minutes. The precipitate was filtered and washed with diethyl ether to give 44 g (90%) of crude acid (contaminated with adsorbed hydrochloric acid).

The crude acid was dissolved in boiling water (60 mL) followed by the addition of methanol (500 mL) and, immediately, propylene oxide (20 mL). The mixture was cooled to -5°C for 1 hour, and the precipitate was filtered and washed with methanol and diethyl ether to give 40.5 g of tert-butylaminemethylphosphonic acid, white needles, mp, 295°C dec (Moedritzer, K., op .Cit.) 289 °C decomposition); 1 H NMR (D 2 O) δ 1.31 (s, 9H), 3.03 (d, J = 13.9 Hz, 2H); 13 C NMR δ 23.9, 37.6 (d, J = 137.4 Hz), 58.1 (d, J = 7.4 Hz).

Disodium tert-butylamine methylphosphonate

Tert-butylamine methylphosphonic acid (18.4 g, 0.11 mol) was added sodium hydroxide (8.8 g, 0.22 mol solution in methanol (100 mL). The mixture was stirred at reflux for 2 hours. The mixture was concentrated in vacuo until solid (about 1/3 volume) and diethyl ether was added (200 mL).The precipitate was filtered and washed with diethyl ether to give disodium tert-butylamine methylphosphonate (20 g, 86%), white microcrystals, dec 350 °C; 1H NMR (D2O) δ 1.02 (s, 9H), 2.47 (d, J = 15.0 Hz, 2H); 13C NMR δ 26.4, 40.1 (d, J = 136.3 Hz ), 50.6 (d, J = 12.0 Hz).

EXPERIMENTAL PROCEDURE

1. Absorption tests were performed at 35°C on 0.15 molar aqueous solutions of absorbent using a nitrogen:carbon dioxide:hydrogen sulfide gas mixture of 89:10:1 for 2 hours.

2. Desorption experiments were performed at 85 °C in flowing nitrogen for 2 h at the same flow rate as the test gas mixture.

The absorbents tested and the absorption results for both fresh absorbent and regenerated absorbent are presented in Table 1

TABLE 1

Selectivity = (H2S/CO2) in solution/(H2S/CO2) in feed gas Load = mol H2S/mol absorbent compound Capacity =

Claims (14)

Patent claims 1. Process for the selective absorption of H2S from gaseous mixtures of said H2S, non-acidic components and CO2 by contacting said mixture with an amine-containing absorbent solution comprising: a metal sulfonate of at least one blocked secondary or tertiary amine, wherein the metal sulfonate is bound to the amino nitrogen through an alkylene group containing at least one carbon atom and where the amino nitrogen is substituted with at least one C4-C6 straight or branched alkyl chain, under conditions whereby H2S is selectively absorbed from said mixture. 2. Method according to claim 1, in which the absorbent solution comprises an absorbent having the formula: wherein R 1 is a C 4 -C 6 straight or branched alkyl chain; R2, R3 and R4 are the same or different, and are selected from hydrogen, C1-C9 substituted or unsubstituted alkyl, C3-C9 substituted or unsubstituted branched alkyl, C3-C9 cycloalkyl, C6-C9 aryl, alkylaryl or arylalkyl, C2-C9 straight or branched hydroxyalkyl, hydroxycycloalkyl and mixtures thereof; and wherein when n is 2 or more, R 3 and R 4 on an adjacent carbon atom or carbon atoms separated by one or more carbon atoms may be a cycloalkyl or aryl ring, and wherein, when substituted, the substituents are heteroatom-containing substituents, n is an integer of 1 or more, and the metal cation is a monovalent, divalent or trivalent metal cation sufficient to satisfy the valence requirement for the anions or anion cluster. 3. Process according to claim 2, where R2 is selected from H, C4-C6 substituted or unsubstituted straight or branched alkyl, cycloalkyl, C6-C7 aryl, alkylaryl, arylalkyl, C4-C6 straight or branched hydroxylalkyl, cycloalkyl and mixtures thereof , preferably C4-C6 straight or branched alkyl, more preferably tertiary butyl. 4. Method according to claim 2, where n is 2 to 4. 5. A method according to any one of claims 1 to 4, wherein R 1 is a tertiary butyl. 6. Use of selective absorption of H2S from gaseous mixtures of said H2S, non-acid components and CO2 by an absorbent comprising a metal sulfonate of at least one blocked secondary or tertiary amine, wherein the metal sulfonate is bound to the amino nitrogen through an alkylene group containing at least one carbon atom and where the amino nitrogen is substituted with at least one C4-C6 straight or branched alkyl chain. 7. Use according to claim 6, in which the absorbent has the formula: wherein R 1 is a C 4 -C 6 straight or branched alkyl chain; R2, R3 and R4 are the same or different, and are selected from hydrogen, C1-C9 substituted or unsubstituted alkyl, C3-C9 substituted or unsubstituted branched alkyl, C3-C9 cycloalkyl, C6-C9 aryl, alkylaryl or arylalkyl, C2-C9 straight or branched hydroxyalkyl, hydroxycycloalkyl and mixtures thereof; and wherein, when n is 2 or more, R 3 and R 4 on adjacent carbon atom or carbon atoms separated by one or more carbon atoms, may be a cycloalkyl or aryl ring, and wherein, when substituted, the substituents are heteroatom-containing substituents, n is an integer of 1 or more, and the metal cation is a monovalent, divalent or trivalent metal cation sufficient to satisfy the valence requirement for the anions or anion cluster. 8. Use according to claim 7, where R2 is selected from H, C4-C6 substituted or unsubstituted straight or branched alkyl, cycloalkyl, C6-C7 aryl, alkylaryl, arylalkyl, C4-C6 straight or branched hydroxylalkyl, cycloalkyl and mixtures thereof, preferred C4-C6 straight or branched alkyl, more preferably tertiary butyl. 9. Use according to claim 7, where n is 1 to 4, preferably 2 to 4. 10. Use according to any one of claims 6 to 9, wherein R 1 is a tertiary butyl. 11. Absorbents for selective absorption of H2S from mixtures comprising said H2S, gaseous non-acid components and CO2, said absorbents comprising a metal sulfonate of at least one blocked secondary or tertiary amine, wherein the metal sulfonate is bound to the amino nitrogen through an alkylene group containing at least one carbon atom and where the amino nitrogen is substituted with at least one tertiary butyl. 12. Absorbent according to claim 11 with the formula: wherein R 1 is a tertiary butyl; R2, R3 and R4 are the same or different, and are selected from hydrogen, C1-C9 substituted or unsubstituted alkyl, C3-C9 substituted or unsubstituted branched alkyl, C3-C9 cycloalkyl, C6-C9 aryl, alkylaryl or arylalkyl, C2-C9 straight or branched hydroxyalkyl, hydroxycycloalkyl and mixtures thereof; and wherein when n is 2 or more, R 3 and R 4 on adjacent carbon atom or carbon atoms separated by one or more carbon atoms may be a cycloalkyl or aryl ring, and wherein, when substituted, the substituents are heteroatom-containing substituents, is n an integer of 1 or more, and metal cation is monovalent, divalent or trivalent metal cation sufficient to satisfy the valence requirement for the anions or anion cluster. 13. Absorbent according to claim 12, where R2 is selected from H, C4-C6 substituted or unsubstituted straight or branched alkyl, cycloalkyl, C6-C7 aryl, alkylaryl, arylalkyl, C4-C6 straight or branched hydroxylalkyl, cycloalkyl and mixtures thereof, preferred C4-C6 straight or branched alkyl, more preferably tertiary butyl. 14. Absorbent according to claim 12, where n is 1 to 4, preferably 2 to 4.